We report the development and evaluation of a simple, inexpensive sensor capable of detecting liquid D2O and other isotopologues of liquid water through the measurement of electrical signals generated from a nano-porous alumina film. This electrical output, consisting of a sharp voltage pulse followed by a separate broad voltage pulse, is present during the application of microliter volumes of liquid. The amplitude and temporal characteristics of these pulses have been combined to enable four diagnostic parameters used for the sensing of D2O and H218O. The sensing mechanism is based on spatially localized variations in the surface potential of alumina, induced by isotopically substituted water molecules, combined with the effect of isotopic composition on charge transfer to the sensor. As a proof-of concept demonstration, a sensing system has been developed that provides real-time detection of liquid D2O in a stand-alone system.